Population processes at the grassland-scrub interface

The flora of central Europe is rich in species of calcareous grasslands and of scrub. In the same area the natural vegetation before human interference was predominantly forest in which the majority of these species were probably confined to temporary openings of the canopy (gaps), or to forest edges where trees are excluded for edaphic or climatic reasons (rocky outcrops, alpine timberline, riversides). Shrubs and herbaceous species of these primary edges became abundant under human influence in extensively used grasslands, hedgerows and scrublands. At these sites the grassland-scrub edge shifts spatially depending on the intensity of agricultural management, i. e. either cutting of woody species or abandonment of grassland. Primary forest edges, on the other hand, are long-lasting habitats with only minor successional changes, but even here temporary shifts of the edge are to be expected after hurricanes, fire, floods or unusual drought which are detrimental for woody species. The vegetation of primary and secondary forest edges has been frequently described. However, studies of the population processes along and across these ecotones are scarce, although these processes are of pivotal importance for the response of grassland and scrub communities to changes in the edge structure. This contribution reviews research on population dynamics at the grassland-scrub interface. The results arc discussed with respect to management and to nature conservation.